In certain types of weaving machines, i.e., shuttleless or air-jet looms, the weft thread to be intermittently inserted into the shed is correspondingly withdrawn from a supply bobbin in time-spaced intervals. The resulting pulling impulses of the thread yield an undesirable variation in tension on the strand, and serves to set up short-term longitudinal oscillations in the strand tension.
Such effects have been found to adversely affect the operation of the weft insertion mechanism of the associated shuttleless loom, and thereby leads to a diminution in the quality of the woven fabric.
In an attempt to avoid such disadvantages, certain types of strand-braking mechanisms have been inserted between the supply bobbin and the weft insertion portion of the associated loom. In one advantageous design of this type, the strand is advanced along the upper surface of a guide plate which is contacted at spaced longitudinal portions therealong by means of resilient arms, such arms serving to exert a certain contact pressure on the advancing strand. A plurality of strand-guiding eyelets are positioned between successive ones of the resilient arms at the inlet portion of the braking mechanism, whereby the strand follows a serpentine path between successive ones of the resilient arms through the intervening eyelet.
Unfortunately, when such designs are employed in systems having a relatively large variation in tension, an auxiliary braking mechanism must be disposed upstream of the inlet end thereof to exert a pre-equalization effect. Moreover, such designs lack flexibility in the fine adjustment of the contact pressure exerted on the strand by the successive resilient arms.